The present invention relates to an electronic device, in particular a car radio, that has a microprocessor and operating buttons that can be lighted using light sources.
Such electronic devices are used in particular as consumer electronics equipment, which should be operable even in low light. The night design of car radios has the function of allowing the operating buttons to be located and operated in an essentially dark interior of an motor vehicle in the absence of daylight.
At the present time, operating buttons in car radios are usually designed as short-stroke jog keys with analysis of a switch pulse or through conducting rubber mats that establish constant contact and are responsible for the restoring force of the buttons.
The conventional operating buttons must have a reliable mechanical and electric design. Mechanical wear on contacts or the conducting rubber of the rubber mats is the deciding factor in the required service life of these buttons. To reliably achieve the required long service life, the operating buttons must have a relatively expensive design, so they are a cost-determining element that cannot be disregarded for car radios.
An object of the present invention is to create a design for operating buttons of an electronic device that will permit a long service life of the operating buttons at a reduced cost.
This object is achieved according to the present invention by an electronic device in which the light sources can be supplied cyclically with control pulses in succession as controlled by the microprocessor; the operating buttons each have a light receiver arrangement optically connectable to the light source, such that its optical connection to the light source can be changed by operating the respective operating button; and the microprocessor is equipped for allocation of the output signals of the light receiver arrangements to the cyclically emitted pulses.
The lighting function for the operating buttons is combined with detection of button operation according to the present invention. In contrast with the implementations generally used for car radios and similar electronic devices, button operation is detected not electrically but instead with the help of the light used for illumination. To make this possible, this illumination light is generated in the form of light pulses in such rapid succession that the human eye perceives the illumination provided by each light source as being continuous. Such pulses in a high frequency cycle are distributed cyclically to the light sources as controlled by the microprocessor, so that one light source is assigned to each control pulse. Thus, on the basis of the output signals of the light receiver arrangements arriving at the microprocessor, the microprocessor can determine the instantaneous operating status of the operating buttons correlating with a certain control pulse; the microprocessor does this by determining whether a pulse of the light receiver arrangement corresponding to the output control pulse reaches its input. Within the scope of the arrangement according to the present invention, it is also readily possible to implement a dimmer function by varying the clock frequency of the microprocessor or by varying the pulse widths of the cyclically distributed control pulses.
In an advantageous embodiment of the present invention, the light sources are connected to outputs of a shift register, which is in turn connected to a clock pulse output of the microprocessor. The cyclic distribution of the control pulses takes place by way of the shift register which is clocked by the microprocessor. Furthermore, the shift register is connected to a reset output of the microprocessor, so that the shift register is reset to a defined starting state after scanning the operating buttons to guarantee secure allocation of clock pulse numbers of the microprocessor to the control pulses sequentially distributed to the individual light sources in succession by way of the shift register.
The light receiver arrangement of an operating button has a fiber-optic arrangement. This makes it possible to analyze received light from all the operating buttons jointly, e.g., by sending the light to a common optoelectric receiver, thus yielding a very simple and inexpensive analyzer arrangement.
A displacement motion of the operating button can be utilized for detection of the operating status of the operating button. It is also possible within the scope of the present invention to use operating buttons that can be operated without any displacement motion. In this case the reflectivity of the operating finger of a person operating the button can be used in a conventional manner in that the illuminating light emanating from the operating button is reflected by the operating finger into an end face of a fiber-optic cable. For specially shaped key depressions, it is also conceivable to establish a permanent optical connection between the light exit point and the end face of a fiber-optic arrangement, which is interrupted by a finger operating the operating button.
For a high reliability in detecting the operating status of the operating button with a very simple arrangement, a fiber-optic segment is arranged in each operating button for constantly receiving a light component of the light source, the operating button is displaceable for operation, and the displacement motion of the operating button causes displacement of the fiber-optic segment relative to a fiber-optic cable leading away from the operating button. Depending on the operating status of the operating button, the light collected by the fiber-optic segment is diverted in the fiber-optic cable or does not reach the fiber-optic cable. Since the optical fibers may be very thin, only a very small displacement motion is needed to be able to detect the operating status reliably. It is advantageous for the optical connection between the fiber-optic segment and the fiber-optic cable to be interrupted when the operating button is depressed, because in this way proper functioning of the arrangement can be checked by the microprocessor when the operating button is at rest.